EFFECT OF WEAVE STRUCTURE ON TENSILE STRENGTH AND YARN CRIMP OF THREE-DIMENSIONAL FIBRE WOVEN FABRIC.
Three-dimensional (3D) woven fabric as reinforcement is backbone of composites and becoming the material preferred due to cost saving, high production, near-net shaping and superior mechanical properties. It is very important to determine the mechanical properties of a 3D woven fabric before proposing the particular end use. It may be achieved by utilising a complex engineering data to develop models which can predict the failure mechanism. This paper presents the influence of weave structure on tensile strength of 3D carbon Fibre woven fabric. Three different structures layer to layer, orthogonal and angle interlock weaves have been used. Effect of weave has been investigated in both longitudinal (warp) and horizontal (weft) direction. The effect of crimp on failure mechanism was also studied. It is observed that the crimp interchange between the carbon tows and the binder yarn leads to decreasing load over the fibres (warp and weft).
As a result, strength and stiffness may be increased. Layer to layer weave structure was found to have higher strength and moduli (in warp) as well as strength as compared to orthogonal and angle interlock weaves.
Keyw:ords 3D woven fabrics, Tensile strength, Weave designs, Undulation of yarn
Textile composite material is one of the promising technologies and its application is tremendously increasing day by day in various fields such as aerospace, marine, automotive [1-4] etc. Three dimensional (3D) woven fabric as reinforcement is the backbone of textile composites and becoming popular due to cost saving, high production, near-net shaping and superior mechanical properties [5-11]. The 3D textile composites have reasonably resistance to crack propagation due to heavy tow interlacement. In addition they have better delamination, toughness, impact damage resistance and post-impact mechanical properties than conventional laminated composites [12, 13]. Fully interlaced 3D fabric comprising high performance fibres have the potential of changing the way composite structures are designed and built. Aircraft manufacturers have been continuously increasing the utilization of composite materials in their efforts to reduce weight .
The recent example of composite growth is the Boeing 787 Dreamlinear in which composite material is used 50% by weight and 70% by volume. The potential characteristics of 3D woven fabrics have led to aerospace structures, automotive, marine and many more applications. Currently these materials are used in wing connectors, missile nose cones, components of scramjet engines fuselage frames and multi blade stiffened panels . These uses are because of their outstanding physical, thermal and mechanical properties particularly high stiffness and strength to weight ratio, fatigue strength, excellent corrosion resistance and dimensional stability. Generally, the 3D woven fabrics are suitable and successful for structural application  due to having multilayer, stuffer yarn and through thickness reinforcement. However, the application of 3D woven fabric is still narrowed due to be deficiency in understanding the influence of weaving parameters on architecture and mechanical properties of the composites [16-18].
It is very important to determine the mechanical properties of 3D woven fabric before proposing the end use. The most important properties of textile composites are in-plane shear, tensile behaviour and through the thickness compaction .
There are number of deformation mechanisms available for the textile reinforcing material. It may be achieved by generating huge engineering data to predict the model which can define the failure mechanism. Few models have been proposed to predict the in-plane elastic properties of composite materials [20, 21]. Nevertheless, none of these is capable to predict failure mechanism of 3D woven fabric for composites. Some work has been done for tensile properties [8, 22-24] with limited scope and fibre architecture in fabric which shows that 3D woven has superior strength over 2D woven fabric. This paper presents the tensile evaluation of 3D woven structures (orthogonal, angle interlock and layer to layer). The crimp of each 3D woven structure has been analysed with reference to their orientation. Tensile strength has been examined by using Instron tensile testing equipment. Measured values of tensile strength are compared and discussed.
MATERIAL AND METHODS
3D Woven Fabrics: Three structures of 3D woven fabric made of carbon fibres are used in this study. The three weaves which are used in this study are orthogonal, layer to layer and angle interlock (Fig.1). The specifications of 3D woven fabrics used in this study are presented in Table 1.
Methods: To investigate the effect of weave structure on tensile strength and modulus in the longitudinal and transverse directions, the yarns (warp, weft and binders) distribution are kept equal in all directions (see Table 1) so that failure behaviour can be analysed with regard to weave structure.
Table 1. Specification of 3D Fabrics
Fabric Structure###Areal Density###No. of###No. of###No. of
###per cm###per cm###per cm
Layer to Layer###1960.72###2###4###3
Measurement of Yarn Crimp: Yarn orientation and crimp (Fig. 2) are the most important factors that make strong influence on mechanical properties of 3D fabric. Therefore, crimp in 3D woven fabric was determined in accordance with BS ISO 7211-3:1984. Crimp tests were carried out for each yarn (warp weft and binder) to analyse the role and impact on strength of each of 3D weaves. Minimum five samples of 100 mm length have been used to measure yarn crimp measurement for every yarn.
Measurement of Tensile Strength and Modulus: Tensile strength and modulus of 3D woven fabric samples were determined in accordance with British Standard BS EN ISO 13934-1:1999 on a Zwick Instron testing machine with a load cell capacity of 10KN. The tensile strength was tested on both longitudinal and transverse directions of 3D woven fabrics in order to record the strength and modulus in both directions. For every direction, minimum five samples were used. The sample size was 200 x 50 mm (gauge length 100 mm) and cross head speed was 20 mm/min for all samples.
RESULTS AND DISCUSSION
Yarn Crimp: Yarn crimp has direct relationship with mechanical properties particularly strength of textile fabric.
The stiffness of fabric decreases with increasing yarn crimp [25,26]. Crimp is also related to material strength [25,27]. When the load is applied on 3D woven fabric and if the tows are straight and non-crimped then full load will be faced in tension at complete strength. However, if tows have got crimp or bent then the initial load will be consumed in straightening bent tows and then take up load and subsequently leads to low strength material .
Fig. 3 compares the crimp percentage of warp, weft and binder of selected 3D woven structures. Crimp values of preform were calculated using BS ISO 7211-3:1984. It is seen that among the all types of yarns (warp, weft and binder), weft yarn contributes small quantity of crimp in all 3D woven structures and binders add significant amount of crimp along the length of fabric. Binder yarn in layer to layer weave has highest amount of crimp among all weaves due to; binder yarn wrap around a relatively straight yarn (weft). As a result, warp and weft yarn of layer to layer carry smallest crimp amount in their respective categories.
Tensile Strength Analysis of 3D Woven Structures: The typical tensile force and strain curves of the warp and weft direction for all the weaves are shown in Figs. 4 and 5. It can be observed that the load and strain curves exhibit largely linear behavior. The test data are summarized in Table 2 and 3, and it is seen that the E-modulus of all 3D weave structures had higher values in the warp direction than those in the weft direction.
When the specimens are subjected to tension along the warp direction, the tensile loads are primarily carried by warp yarns, thus the straightening tendency of warp yarns will cause high values of stresses in yarn crossover areas. Such stress concentrations can trigger localized damage in warp yarn even when the overall applied tensile stress is much lower than the ultimate tensile strength. This can well explain why the fracture of warp yarns mostly occurred in yarn crossover areas.
Table 2. Measured Values of Warp Wise Tensile Strength of the 3D Fabrics
###Strain at Fmax###Maximum###Work at###E-Modulus
Layer to Layer###8.96198###7798.57###33810.5###2443790
Table 3. Measured Values ff Weft Wise Tensile Strength of the 3D Fabrics
###Strain at Fmax###Maximum###Work at###E-Modulus
Layer to Layer###7.51156###8938.75###27436###1772240
Same behaviour is seen in the layer to layer weave. This weave design has much higher curve than all the other weave designs (see Fig. 04). Layer to layer weave has carried highest load as well strain in warp direction comparing other weaves. It may be because of the numbers of layers (higher density) and the crimp present in the yarn. In addition to, layer to layer weave has lowest failure to strain in weft direction (see Fig. 05) comparing other weaves and strain of layer to layer in warp due to low amount of crimp present in weft direction. Similarly, orthogonal weave has got higher strength in weft direction comparing to warp direction due to low waviness present in weft yarn.
The load-strain curve of angle interlock warp and weft direction is appears to be similar to the orthogonal weave but the E-Modulus are different for both the weaves. It may be for the reason that the weave designs in the orthogonal the binder yarn passes linearly and in the angle interlock weave the binder yarns are travelling along angle so the strength will be affected.
In this research, the effect of weave structure on tensile strength of 3D carbon fibre woven fabric was examined. Three different weave structures (layer to layer, angle interlocked and orthogonal) considered to analyse the effect of yarn orientation and crimp on 3D woven fabric. Specimens of each weave have been tested in horizontal (weft) and longitudinal (warp) for tensile testing and results are presented.
It is observed that crimp plays vital role for tensile properties of 3D weave. However if waviness of load taking yarn may be shifted towards binder yarns may decrease the crimp of load taking fibre (warp and weft); as a result, strength and stiffness may be increased. This phenomenon can clearly be seen in layer to layer structure.
The load-strain curves are almost linear in all weaves. Layer to layer weave structure has got highest E-modulus (in warp) as well as strength as compared to orthogonal and angle interlock weaves. Since, orthogonal and angle interlock weave have got more or less same failure behaviour. However, angle interlock has got higher failure to strain.
The authors would like to thank Dr Prasad Potluri for his support, and gratefully acknowledge the facilities provided by University of Manchester UK to carry out the experimental work.
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Department of Textile Engineering, Mehran University of Engineering and Technology, Jamshoro.,
Department of Textiles and Paper, School of Materials, University of Manchester, UK
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|Author:||Peerzada, Mazhar Hussain; Abbasi, Sadaf Aftab; Khatri, Awais|
|Date:||Mar 31, 2012|
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